I've done a late model roller cam retrofit (98 Z28) into a '66 327 block based on detailed photo's and descriptions I picked up off of ebay a few years back (I think; it's been a lonnnnng term project). SSendan64, sounds like you might even be the author based on the description of the spacers.
Anyway it uses GM 4.3L hydraulic lifters and involved some minor grinding here and there. I'm setting the engine up on a test stand to break it in. Will be interesting (to say the least) to see how things work out, since this is very eclectic and not in any book.